The present invention relates to a novel pyrimidine nucleoside derivative and an antiviral agent containing the derivative as active ingredient.
Infectious diseases caused by human acquired immunodeficiency virus (HIV), which is a type of retrovirus, have recently become a serious social problem. A compound of 3'-deoxy-3'-azidothymidine is known as a nucleoside compound used in the clinical treatment for diseases caused by HIV-infection. However, this compound has side-effects since it also exhibits considerable strong toxicity in the host cells.
Although some 2',3'-dideoxyribonucleosides are known as nucleoside compounds exhibiting an anti-retroviral activity, it is still necessary to develop a substance possessing a higher activity and lower toxicity to the host cell (Hiroaki Mitsuya, Bodily Defence, Vol. 4, pp. 213-223 (1987)).
On the other hand, various acyclonucleoside compounds have been synthesized since Acyclovir (acycloguanosine) was developed as an antiviral substance effective against herpes virus (C. K. Chu and S. J. Culter, J. Heterocyclic Chem., 23, p. 289 (1986)). However, no compound having a sufficient activity especially against retroviruses has yet been discovered.
Consequently, with the aim of providing an antiviral agent, especially an agent which has an effective antiviral activity against retroviruses, the present inventors have synthesized a wide variety of novel 6-substituted acyclopyrimidine nucleoside compounds and their anti-retroviral activities have been investigated. As the results, the present inventors have found that such an object can be attained by a specific 6-substituted acyclopyrimidine nucleoside derivative (WO 89/09213).
As 6-substituted acyclopyrimidine nucleosides, 6-fluorine substituted derivatives and 6-alkylamino substituted derivatives (DD-A-232492) and 6-methyl substituted derivatives (C.A. 107, 129717w (1987)) are known, however, the antiviral activity of these compounds has not been described.
The present inventors have conducted intensive studies on the screening of compounds having antiviral activities, especially a compound having an anti-retroviral activity, and found that among the 6-substituted acyclopyrimidine nucleoside derivatives generically disclosed but not specifically disclosed in WO 89/09213, those pyrimidine nucleoside derivatives having ethyl group or isopropyl group at the 5-position of the pyrimidine ring and having (substituted) phenylthio group or (substituted) benzyl group showed markedly excellent anti-retroviral activities. The present invention has been accomplished based on this finding.